AX5243 Advanced High Performance ASK and FSK Narrow-band Transceiver for 27 - 1050 MHz Range

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Advanced High Performance ASK and FSK Narrow-band Transceiver for

27 - 1050 MHz Range

OVERVIEW

The AX5243 is a true single chip ultra−low power narrow−band CMOS transceiver for use in licensed and unlicensed bands from 27 and 1050 MHz. The on−chip transceiver consists of a fully integrated RF front−end with modulator, and demodulator. Base band data processing is implemented in an advanced and flexible communication controller that enables user friendly communication via the SPI interface.

Features

Advanced Multi−channel Narrow−band Single Chip UHF Transceiver (FSK / MSK / 4−FSK / GFSK / GMSK / ASK / AFSK / FM / PSK)

Low−Power

•

^RX

9.5 mA @ 868 MHz and 433 MHz 6.5 mA @ 169 Hz

•

TX at 868 MHz 7.5 mA @ 0 dBm 16 mA @ 10 dBm 48 mA @ 16 dBm

•

50 nA Deep Sleep Current

•

500 nA Power−down Current with Low Frequency Duty Cycle Clock Running

Extended Supply Voltage Range

•

1.8 V − 3.6 V Single Supply

High Sensitivity / High Selectivity Receiver

•

Data Rates from 0.1 kbps to 125 kbps

•

Optional Forward Error Correction (FEC)

•

Sensitivity without FEC

−135 dBm @ 0.1 kbps, 868 MHz, FSK

−126 dBm @ 1 kbps, 868 MHz, FSK

−107 dBm @ 100 kbps, 868 MHz, FSK

−105 dBm @ 125 kbps, 868 MHz, FSK

•

Sensitivity with FEC

−137 dBm @ 0.1 kbps, 868 MHz, FSK

•

High Selectivity Receiver with up to 45 dB Adjacent Channel Rejection

•

0 dBm Maximum Input Power

•

^>±10% Data−rate Error Tolerance

•

Short Preamble Modes Allow the Receiver to Work with as little as 16 Preamble Bits

•

Fast State Switching Times 200 ms TX → RX Switching Time 62 ms RX → TX Switching Time Transmitter

•

Data−rates from 0.1 kbps to 125 kbps

•

High Efficiency, High Linearity Integrated Power Amplifier

•

Maximum Output Power

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ORDERING INFORMATION

Device Type Qty

AX5243−1−TA05 Tape & Reel 500 AX5243−1−TW30 Tape & Reel 3,000

QFN20 4x4, 0.5P CASE 485EE

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Frequency Generation

•

Configurable for Usage in 27 MHz −1050 MHz Bands

•

RF Carrier Frequency and FSK Deviation Programmable in 1 Hz Steps

•

Ultra Fast Settling RF Frequency Synthesizer for Low−power Consumption

•

Fully Integrated RF Frequency Synthesizer with VCO Auto−ranging and Band−width Boost Modes for Fast Locking

•

Configurable for either Fully Integrated VCO, Internal VCO with External Inductor or Fully External VCO

•

Configurable for either Fully Integrated or External Synthesizer Loop Filter for a Large Range of Bandwidths

•

Channel Hopping up to 2000 hops/s

•

Automatic Frequency Control (AFC) Flexible Antenna Interface

•

Integrated RX/TX Switching with Differential Antenna Pins

Wakeup−on−Radio

•

640 Hz or 10 kHz Lowest Power Wake−up Timer

•

Wake−up Time Interval Programmable between 98ms and 102 s

Sophisticated Radio Controller

•

Fully Automatic Packet Reception and Transmission without Micro−controller Intervention

•

Supports HDLC, Raw, Wireless M−Bus Frames and Arbitrary Defined Frames

•

Automatic Channel Noise Level Tracking

•

ms Resolution Timestamps for Exact Timing (eg. for Frequency Hopping Systems)

•

256 Byte Micro−programmable FIFO, optionally Supports Packet Sizes > 256 Bytes

•

Three Matching Units for Preamble Byte, Sync−word and Address

•

Ability to store RSSI, Frequency Offset and Data−rate Offset with the Packet Data

•

Multiple Receiver Parameter Sets Allow the Use of more Aggressive Receiver Parameters during Preamble, dramatically Shortening the Required Preamble Length at no Sensitivity Degradation

Advanced Crystal Oscillator

•

Fast Start−up and Lowest Power Steady−state XTAL Oscillator for a Wide Range of Crystals

•

Integrated Crystal Tuning Capacitors

•

Possibility of Applying an External Clock Reference (TCXO)

Miscellaneous Features

•

Few External Components

•

SPI Microcontroller Interface

•

Extended Register Set

•

Fully Integrated Current/Voltage References

•

QFN20 4 mm x 4 mm Package

•

Internal Power−on−Reset

•

Brown−out Detection

•

10 Bit 1 MS/s General Purpose ADC (GPADC) Applications

27 − 1050 MHz Licensed and Unlicensed Radio Systems

•

Internet of Things

•

Automatic Meter Reading (AMR)

•

Security Applications

•

Building Automation

•

Wireless Networks

•

Messaging Paging

•

Compatible with: Wireless M−Bus, POCSAG, FLEX, KNX, Sigfox, Z−Wave, enocean

•

Regulatory Regimes: EN 300 220 V2.3.1 including the Narrow−band 12.5 kHz, 20 kHz and 25 kHz

Definitions; EN 300 422; FCC Part 15.247; FCC Part 15.249; FCC Part 90 6.25 kHz, 12.5 kHz and 25 kHz

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BLOCK DIAGRAM

Figure 1. Functional Block Diagram of the AX5243

AX5243

3 ANTP ANTN 4

IF Filter &

AGC PGAs

AGC

Crystal Oscillator

typ.

16 MHz

FOUT

FXTAL

Communication Controller &

Serial Interface

Divider

ADC

Digital IF channel

filter LNA

PA diff

De- modulator

Encoder Framing FIFO

Modulator Mixer

20

CLK16P

19

CLK16N

Chip configuration

9

SYSCLK VDD_IO

Voltage Regulator

POR

Low Power Oscillator 640 Hz/10kHz

References

Wake on Radio Registers

14

IRQ

15

TCXO_EN

1,5 16

VDD_ANA

6

FILT

7

L1

RF Frequency Generation Subsystem RF Output 27 MHz – 1.05 GHz

8

L2

GPADC1 Forward E Correct

rror

17 18

GPADC2 ion Ra Controlledior timing and packet handling

10

SEL

11

CLK

12

MISO

13

MOSI

SPI

FIFO

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Table 1. PIN FUNCTION DESCRIPTIONS

Symbol Pin(s) Type Description

VDD_ANA 1 P Analog power output, decouple to neighboring GND

GND 2 P Ground, decouple to neighboring VDD_ANA

ANTP 3 A Differential antenna input/output

ANTN 4 A Differential antenna input/output

VDD_ANA 5 P Analog power output, decouple to GND

FILT 6 A Optional synthesizer filter

L2 7 A Optional synthesizer inductor, should be shorted with L1 if not used.

L1 8 A Optional synthesizer inductor, should be shorted with L2 if not used.

SYSCLK 9 I/O Default functionality: Crystal oscillator (or divided) clock output Can be programmed to be used as a general purpose I/O pin Selectable internal 65 kW pull−up resistor

SEL 10 I Serial peripheral interface select

CLK 11 I Serial peripheral interface clock

MISO 12 O Serial peripheral interface data output

MOSI 13 I Serial peripheral interface data input

IRQ 14 I/O Default functionality: Transmit and receive interrupt

Can be programmed to be used as a general purpose I/O pin Selectable internal 65 kW pull−up resistor

TCXO_EN 15 I/O General purpose I/O pin which can be programmed to enable an

external TCXO

Selectable internal 65 kW pull−up resistor

VDD_IO 16 P Power supply 1.8 V – 3.3 V

GPADC1 17 A GPADC input, must be connected to GND if not used

GPADC2 18 A GPADC input, must be connected to GND if not used

CLK16N 19 A Crystal oscillator input/output

CLK16P 20 A Crystal oscillator input/output

GND Center pad P Ground on center pad of QFN, must be connected

A = analog input I = digital input signal O = digital output signal I/O = digital input/output signal N = not to be connected P = power or ground

All digital inputs are Schmitt trigger inputs, digital input and output levels are LVCMOS/LVTTL compatible and 5 V tolerant.

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Pinout Drawing

Figure 2. Pinout Drawing (Top View)

1 2 3 4 5

VDD_ANA GND

ANTN VDD_ANA ANTP

MISO MOSI

11 15 14 13 12

IRQ TCXO_EN

CLK

9 10 8 7 6

19 18 17 16 20

CLK16P GPADC1CLK16N GPADC2 VDD_IO

AX5243

Exposed center pad of the QFN package: GND

FILT L2 L1 SYSCLK SEL

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SPECIFICATIONS

Table 2. ABSOLUTE MAXIMUM RATINGS

Symbol Description Condition Min Max Units

VDD_IO Supply voltage −0.5 5.5 V

IDD Supply current 200 mA

Ptot Total power consumption 800 mW

P_i Absolute maximum input power at receiver input ANTP and ANTN

pins in RX mode 10 dBm

I_I1 DC current into any pin except ANTP, ANTN −10 10 mA

I_I2 DC current into pins ANTP, ANTN −100 100 mA

I_O Output Current 40 mA

V_ia Input voltage ANTP, ANTN pins −0.5 5.5 V

Input voltage digital pins −0.5 5.5 V

V_es Electrostatic handling HBM −2000 2000 V

T_amb Operating temperature −40 85 °C

T_stg Storage temperature −65 150 °C

T_j Junction Temperature 150 °C

Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected.

1. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

DC Characteristics Table 3. SUPPLIES

Symbol Description Condition Min Typ Max Units

TAMB Operational ambient temperature −40 27 85 °C

VDD_IO I/O and voltage regulator supply voltage 1.8 3.0 3.6 V

VBOUT Brown−out threshold Note 1 1.3 V

I_DSLLEP Deep Sleep current:

All analog and digital functions are powered down

PWRMODE = 0x01 50 nA

I_PDOWN Power−down current:

Register file contents preserved PWRMODE = 0x00 400 nA

IWOR Wakeup−on−radio mode:

Low power timer and WOR

state−machine are running at 640 Hz

PWRMODE = 0x0B 500 nA

I_STANBY Standby−current:

All power domains are powered up, crystal oscillator and references are running

PWRMODE = 0x05 230 mA

I_RX Current consumption RX PWRMODE = 0x09 RF Frequency Subsystem:

Internal VCO and internal loop−fiter

868 MHz, datarate 6 kbps 9.5 mA

169 MHz, datarate 6 kbps 6.5

868 MHz, datarate 100 kbps 11

169 MHz, datarate 100 kbps 7.5

I_TX−DIFF Current consumption TX 868 MHz, 16 dBm, FSK, Note 2 RF Frequency Subsystem:

Internal VCO and loop−filter

48 mA

1. Digital circuitry is functional down to typically 1 V.

2. Measured with optimized matching networks.

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For information on current consumption in complex modes of operation tailored to your application, see the software AX−RadioLab for AX5243.

Note on current consumption in TX mode

To achieve best output power the matching network has to be optimized for the desired output power and frequency. As a rule of thumb a good matching network produces about 50% efficiency with the AX5243 power amplifier although over 90% are theoretically possible. A typical matching network has between 1 dB and 2 dB loss (Ploss). The PA is internally multiplexed with the LNA on pins ANTP and ANTN. Therefore constraints for the RX matching have to be considered for the PA matching.

The current consumption can be calculated as I_TX[mA]+ 1

PA_efficiency 10^Pout[dBm]10⁾^Ploss[dB]B1.8V)I_offset Ioffset is about 6 mA for the fully integrated VCO at 400 MHz to 1050 MHz, and 3 mA for the VCO with external inductor at 169 MHz. The following table shows calculated current consumptions versus output power for Ploss = 1 dB, PAefficiency = 0.5, Ioffset = 6 mA at 868 MHz and

Ioffset = 3.5 mA at 169 MHz.

Table 4. CURRENT CONSUMPTION VS. OUTPUT POWER

Pout [dBm]

I_txcalc [mA]

868 MHz 169 MHz

0 7.5 4.5

1 7.9 4.9

2 8.4 5.4

3 9.0 6.0

4 9.8 6.8

5 10.8 7.8

6 12.1 9.1

7 13.7 10.7

8 15.7 12.7

9 18.2 15.2

10 21.3 18.3

11 25.3 22.3

12 30.3 27.3

13 36.7 33.7

14 44.6 41.6

15 54.6 51.6

Both AX5243 power amplifiers run from the regulated VDD_ANA supply and not directly from the battery. This has the advantage that the current and output power do not vary much over supply voltage and temperature.

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Table 5. LOGIC

Digital Inputs

VT+ Schmitt trigger low to high threshold point 1.9 V

VT− Schmitt trigger high to low threshold point 1.2 V

VIL Input voltage, low 0.8 V

VIH Input voltage, high 2.0 V

IL Input leakage current −10 10 mA

Rpullup Pull−up resistors

Pins SYSCLK, IRQ, TCXO_EN Pull−ups enabled in the relevant pin configuration registers

65 kW

Digital Outputs

I_OH Output Current, high VDD_IO = 3 V

V_OH= 2.4 V 4 mA

I_OL Output Current, low VDD_IO = 3 V

VOL = 0.4 V 4 mA

I_OZ Tri−state output leakage current −10 10 mA

AC Characteristics

Table 6. CRYSTAL OSCILLATOR

f_XTAL Crystal frequency Note 1, 2, 3 10 16 50 MHz

gm_osc Oscillator transconductance control range Self−regulated see Note 4 0.2 20 mS C_osc Programmable tuning capacitors at pins

CLK16N and CLK16P XTALCAP = 0x00 default 3 pF

XTALCAP = 0x01 8.5 pF

XTALCAP = 0xFF 40 pF

C_osc−lsb Programmable tuning capacitors,

increment per LSB of XTALCAP XTALCAP = 0x01 – 0xFF 0.5 pF

fext External clock input (TCXO) Note 2, 3, 5 10 16 50 MHz

RINosc Input DC impedance 10 kW

NDIVSYSCLK Divider ratio fSYSCLK = fXTAL/ NDIVSYSCLK 2⁰ 2⁴ 2¹⁰

1. Tolerances and start−up times depend on the crystal used. Depending on the RF frequency and channel spacing the IC must be calibrated to the exact crystal frequency using the readings of the register TRKFREQ.

2. The choice of crystal oscillator or TCXO frequency depends on the targeted regulatory regime for TX, see separate documentation on meeting regulatory requirements.

3. To avoid spurious emission, the crystal or TCXO reference frequency should be chosen so that the RF carrier frequency is not an integer multiple of the crystal or TCXO frequency.

4. The oscillator transconductance is regulated for fastest start−up time during start−up and for lowest power during steady state oscillation.

This means that values will depend on the crystal used.

5. If an external clock (TCXO) is used, it should be input via an AC coupling at pin CLK16P with the oscillator powered up and XTALCAP = 0x00.

For detailed TCXO network recommendations depending on the TCXO output swing refer to the AX5243 Application Note: Use with a TCXO Reference Clock.

Table 7. LOW−POWER OSCILLATOR

f_osc−slow Oscillator frequency slow mode LPOSC FAST = 0

No calibration 480 640 800 Hz

Internal calibration vs. crystal

clock has been performed 630 640 650

f_osc−fast Oscillator frequency fast mode LPOSC FAST = 1

No calibration 7.6 10.2 12.8 kHz

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Table 8. RF FREQUENCY GENERATION SUBSYSTEM (SYNTHESIZER)

f_REF Reference frequency The reference frequency must be chosen so that the RF carrier frequency is not an integer multiple of the reference frequency

10 16 50 MHz

Dividers

NDIV_ref Reference divider ratio range Controlled directly with register REFDIV 2⁰ 2³ NDIV_m Main divider ratio range Controlled indirectly with register FREQ 4.5 66.5

NDIV_RF RF divider range Controlled directly with register RFDIV 1 2

Charge Pump

I_CP Charge pump current Programmable in increments of 8.5 mA via

register PLLCPI 8.5 2168 mA

Internal VCO (VCOSEL = 0)

f_RF RF frequency range RFDIV = 1 400 525 MHz

RFDIV = 0 800 1050

f_step RF frequency step RFDIV = 1, f_xtal = 16.000000 MHz 0.98 Hz

BW Synthesizer loop bandwidth The synthesizer loop bandwidth and start−up time can be programmed with registers PLLLOOP and PLLCPI.

For recommendations see the AX5243 Programming Manual, the AX−RadioLab software and AX5243 Application Notes on compliance with regulatory regimes.

50 500 kHz

T_start Synthesizer start−up time if crystal

oscillator and reference are running 5 25 ms

PN868 Synthesizer phase noise 868 MHz

f_REF= 48 MHz 10 kHz offset from carrier −95 dBc/Hz

1 MHz offset from carrier −120

PN433 Synthesizer phase noise 433 MHz

f_REF= 48 MHz 10 kHz offset from carrier −105 dBc/Hz

1 MHz offset from carrier −120

VCO with external inductors (VCOSEL = 1, VCO2INT = 1) f_{RFrng_lo} RF frequency range

For choice of L_ext values as well as VCO gains see Figure 3 and Figure 4

RFDIV = 1 27 262 MHz

f_{RFrng_hi} RFDIV = 0 54 525

PN169 Synthesizer phase noise 169 MHz Lext=47 nH (wire wound 0603) RFDIV = 0, f_REF= 16 MHz Note: phase noises can be improved with higher fREF

10 kHz from carrier −97 dBc/Hz

1 MHz from carrier −115

External VCO (VCOSEL = 1, VCO2INT = 0) fRF RF frequency range fully external

VCO Note: The external VCO frequency needs

to be 2 x f_RF 27 1000 MHz

V_amp Differential input amplitude at L1, L2

terminals 0.7 V

V_inL Input voltage levels at L1, L2

terminals 0 1.8 V

Vctrl Control voltage range Available at FILT in external loop filter

mode 0 1.8 V

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Figure 3. VCO with External Inductors: Typical Frequency vs. L_ext

Figure 4. VCO with External Inductors: Typical K_VCO vs. L_ext

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The following table shows the typical frequency ranges for frequency synthesis with external VCO inductor for different inductor values.

Table 9.

Lext [nH]

Freq [MHz]

RFDIV = 0

Freq [MHz]

RFDIV = 1 PLL Range

8.2 482 241 0

8.2 437 219 15

10 432 216 0

10 390 195 15

12 415 208 0

12 377 189 15

15 380 190 0

15 345 173 15

18 345 173 0

18 313 157 15

22 308 154 0

22 280 140 14

27 285 143 0

27 258 129 15

33 260 130 0

33 235 118 15

39 245 123 0

39 223 112 14

47 212 106 0

47 194 97 14

56 201 101 0

56 182 91 15

68 178 89 0

68 161 81 15

82 160 80 1

82 146 73 14

100 149 75 1

100 136 68 14

120 136 68 0

120 124 62 14

For tuning or changing of ranges a capacitor can be added in parallel to the inductor.

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Table 10. TRANSMITTER

SBR Signal bit rate 0.1 125 kbps

PTX Transmitter power @ 868 MHz Differential PA, 50 W single ended measurement at an SMA connector behind the matching network, Note 2

−10 16 dBm

Transmitter power @ 433 MHz −10 16

Transmitter power @ 169 MHz −10 16

PTX868−step Programming step size output power Note 1 0.5 dB

dTXtemp Transmitter power variation vs.

temperature −40°C to +85°C

Note 2 ±0.5 dB

dTX_Vdd Transmitter power variation vs. VDD_IO 1.8 to 3.6 V

Note 2 ± 0.5 dB

Padj Adjacent channel power

GFSK BT = 0.5, 500 Hz deviation, 1.2 kbps, 25 kHz channel spacing, 10 kHz channel BW

868 MHz −44 dBc

433 MHz −51

PTX868−harm2 Emission @ 2^nd harmonic 868 MHz, Note 2 −40 dBc

PTX868−harm3 Emission @ 3^rd harmonic −60

PTX_433−harm2 Emission @ 2^nd harmonic 433 MHz, Note 2 −40 dBc

PTX_433−harm3 Emission @ 3^rd harmonic −40

1. P_out+TXPWRCOEFFB 2¹²*1 Pmax

2. 50 W single ended measurements at an SMA connector behind the matching network. For recommended matching networks see section: Application Information.

Table 11. RECEIVER SENSITIVITIES

The table lists typical input sensitivities (without FEC) in dBm at the SMA connector with the complete matching network for BER=10⁻3 at 433 or 868 MHz.

Data rate [kbps]

FSK h = 0.66

FSK h = 1

FSK h = 2

FSK h = 4

FSK h = 5

FSK h = 8

FSK

h = 16 PSK

0.1 Sensitivity [dBm] −135 −134.5 −132.5 −133 −133.5 −133 −132.5 −138

RX Bandwidth [kHz] 0.2 0.2 0.3 0.5 0.6 0.9 2.1 0.2

Deviation [kHz] 0.033 0.05 0.1 0.2 0.25 0.4 0.8

1 Sensitivity [dBm] −126 −125 −123 −123.5 −124 −123.5 −122.5 −130

RX Bandwidth [kHz] 1.5 2 3 6 7 11 21 1

Deviation [kHz] 0.33 0.5 1 2 2.5 4 8

10 Sensitivity [dBm] −117 −116 −113 −114 −113.5 −113 −120

RX Bandwidth [kHz] 15 20 30 50 60 110 10

Deviation [kHz] 3.3 5 10 20 25 40

100 Sensitivity [dBm] −107 −105.5 −109

RX Bandwidth [kHz] 150 200 100

Deviation [kHz] 33 50

125 Sensitivity [dBm] −105 −104 −108

RX Bandwidth [kHz] 187.5 200 125

Deviation [kHz] 42.3 62.5

1. Sensitivities are equivalent for 1010 data streams and PN9 whitened data streams.

2. RX bandwidths < 0.9 kHz cannot be achieved with an 48 MHz TCXO. A 16 MHz TCXO was used for all measurements at 0.1 kbps.

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Table 12. RECEIVER

SBR Signal bit rate 0.1 125 kbps

IS_BER868 Input sensitivity at BER = 10⁻³ for 868 MHz operation, continuous data, without FEC

FSK, h = 0.5, 100 kbps −105 dBm

FSK, h = 0.5, 10 kbps −116

FSK, 500 Hz deviation, 1.2 kbps −126

PSK, 100 kbps −109

PSK, 10 kbps −120

PSK, 1 kbps −130

ISBER868FEC Input sensitivity at BER = 10⁻³, for 868 MHz operation, continuous data, with FEC

FSK, h = 0.5, 50 kbps −111 dBm

FSK, h = 0.5, 5 kbps −122

FSK, 0.1 kbps −137

ISPER868 Input sensitivity at PER = 1%, for 868 MHz operation, 144 bit packet data, without FEC

FSK, h = 0.5, 100 kbps −103 dBm

FSK, h = 0.5, 10 kbps −115

FSK, 500 Hz deviation, 1.2 kbps −125

IS_WOR868 Input sensitivity at PER = 1%

for 868 MHz operation, 144 bit packet data, WOR−mode, without FEC

FSK, h = 0.5, 100 kpbs −102 dBm

IL Maximum input level 0 dBm

CP_1dB Input referred compression point 2 tones separated by 100 kHz −35 dBm

RSSIR RSSI control range FSK, 500 Hz deviation, 1.2 kbps −126 −46 dB

RSSIS₁ RSSI step size Before digital channel filter; calculated

from register AGCCOUNTER 0.625 dB

RSSIS₂ RSSI step size Behind digital channel filter; calculated from registers AGCCOUNTER, TRKAMPL

0.1 dB

RSSIS₃ RSSI step size Behind digital channel filter; reading

register RSSI 1 dB

SEL₈₆₈ Adjacent channel suppression 25 kHz channels , Note 1 45 dB

100 kHz channels, Note 1 47

BLK868 Blocking at ±10 MHz offset FSK 4.8 kbps, Note 2 78 dB

RAFC AFC pull−in range The AFC pull−in range can be programmed with the MAXRFOFFSET registers.

The AFC response time can be programmed with the FREQGAIND register.

±15 %

R_DROFF Bitrate offset pull−in range The bitrate pull−in range can be programmed with the MAXDROFFSET registers.

±10 %

1. Interferer/Channel @ BER = 10⁻³, channel level is +3 dB above the typical sensitivity, the interfering signal is CW; channel signal is modulated with shaping

2. Channel/Blocker @ BER = 10⁻³, channel level is +3 dB above the typical sensitivity, the blocker signal is CW; channel signal is modulated with shaping

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Table 13. RECEIVER AND TRANSMITTER SETTLING PHASES

Txtal XTAL settling time Powermodes:

POWERDOWN to STANDBY Note that Txtal depends on the specific crystal used.

0.5 ms

T_synth Synthesizer settling time Powermodes:

STANDBY to SYNTHTX or SYNTHRX 40 ms

Ttx TX settling time Powermodes:

SYNTHTX to FULLTX

T_tx is the time used for power ramping, this can be programmed to be 1 x t_bit, 2 x t_bit, 4 x t_bit or 8 x t_bit.

Notes 1, 2

0 1 x tbit 8 x tbit ms

Trx_init RX initialization time 150 ms

Trx_rssi RX RSSI acquisition time

(after Trx_init) Powermodes:

SYNTHRX to FULLRX Modulation (G)FSK Notes 1, 2

80 + 3 x tbit

ms Trx_preamble RX signal acquisition time to

valid data RX at full sensitivity/selectivity (after T_{rx_init})

9 x t_bit

1. t_bitdepends on the datarate, e.g. for 10 kbps t_bit = 100 ms

2. In wire mode there is a processing delay of typically 6 x t_bit between antenna and DCLK/DATA pins

Table 14. OVERALL STATE TRANSITION TIMES

T_{tx_on} TX startup time Powermodes:

STANDBY to FULLTX Notes 1, 2

40 40 + 1 x t_bit ms

T_{rx_on} RX startup time Powermodes:

STANDBY to FULLRX 190 ms

Trx_rssi RX startup time to valid RSSI Powermodes:

STANDBY to FULLRX Modulation (G)FSK Notes 1, 2

270 +

3 x t_bit ms

T_{rx_data} RX startup time to valid data at full

sensitivity/selectivity 190 +

9 x t_bit ms

T_rxtx RX to TX switching Powermodes:

FULLRX to FULLTX 62 ms

T_txrx TX to RX switching

(to preamble start) Powermodes:

FULLTX to FULLRX 200

T_hop Frequency hop Switch between frequency

defined in register FREQA and FREQB

30 ms

1. t_bitdepends on the datarate, e.g. for 10 kbps t_bit = 100 ms

2. In wire mode there is a processing delay of typically 6 x tbit between antenna and DCLK/DATA pins

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Table 15. SPI TIMING

Tss SEL falling edge to CLK rising edge 10 ns

Tsh CLK falling edge to SEL rising edge 10 ns

Tssd SEL falling edge to MISO driving 0 10 ns

Tssz SEL rising edge to MISO high−Z 0 10 ns

Ts MOSI setup time 10 ns

Th MOSI hold time 10 ns

Tco CLK falling edge to MISO output 10 ns

Tck CLK period Note 1 50 ns

Tcl CLK low duration 40 ns

Tch CLK high duration 40 ns

1. For SPI access during power−down mode the period should be relaxed to 100 ns

For a figure showing the SPI timing parameters see section: Serial Peripheral Interface (SPI).

Table 16. GENERAL PURPOSE ADC (GPADC)

Res Nominal ADC resolution 10 bit

F_conv Conversion rate 0.03 1 MS/s

DR Dynamic range 60 dB

INL Integral nonlinearity ±1 LSB

DNL Differential nonlinearity ±1 LSB

Z_in Input impedance 50 kW

V_DC−IN Input DC level 0.8 V

V_IN−DIFF Input signal range (differential) −500 500 mV

V_IN−SE Input signal range (single−ended, signal input at pin GPADC1, pin GPADC2 open)

300 1300 mV

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CIRCUIT DESCRIPTION

The AX5243 is a true single chip ultra−low power narrow−band CMOS transceiver for use in licensed and unlicensed bands from 27 and 1050 MHz. The on−chip transceiver consists of a fully integrated RF front−end with modulator, and demodulator. Base band data processing is implemented in an advanced and flexible communication controller that enables user friendly communication via the SPI interface.

AX5243 can be operated from a 1.8 V to 3.6 V power supply over a temperature range of −40°C to 85°C. It consumes 7 − 48 mA for transmitting at 868 MHz carrier frequency, 4 – 51 mA for transmitting at 169 MHz depending on the output power. In receive operation AX5243 consumes 9 − 11 mA at 868 MHz carrier frequency and 6.5 − 8.5 mA at 169 MHz.

The AX5243 features make it an ideal interface for integration into various battery powered solutions such as ticketing or as transceiver for telemetric applications e.g. in sensors. As primary application, the transceiver is intended for UHF radio equipment in accordance with the European Telecommunication Standard Institute (ETSI) specification EN 300 220−1 and the US Federal Communications Commission (FCC) standard Title 47 CFR Part 15 as well as Part 90. AX5243 is compliant with respective narrow−band regulations. Additionally AX5243 is suited for systems targeting compliance with Wireless M−Bus standard EN 13757−4:2005. Wireless M−Bus frame support (S, T, R) is built−in.

AX5243 supports any data rate from 0.1 kbps to 125 kbps for FSK, 4−FSK, GFSK, GMSK, MSK, ASK and PSK. To achieve optimum performance for specific data rates and modulation schemes several register settings to configure the AX5243 are necessary, for details see the AX−RadioLab Software which calculates the necessary register settings and the AX5243 Programming Manual.

The AX5243 can be operated in two fundamentally different modes.

Data is sent and received via the SPI port in frames. Pre−

and post−ambles as well as checksums can be generated automatically. Interrupts control the data flow between a micro−controller and the AX5243.

Both transmit and receive use frame mode. In both cases the AX5243 behaves as a SPI slave interface. Configuration of the AX5243 is always done via the SPI interface.

The receiver and the transmitter support multi−channel operation for all data rates and modulation schemes.

Voltage Regulators

The AX5243 uses an on−chip voltage regulator system to create stable supply voltages for the internal circuitry from the primary supply VDD_IO. The I/O level of the digital pins is VDD_IO.

Pins VDD_ANA are supplied for external decoupling of the power supply used for the on−chip PA.

The voltage regulator system must be set into the appropriate state before receive or transmit operations can be initiated. This is handled automatically when programming the device modes via the PWRMODE register.

Register POWSTAT contains status bits that can be read to check if the regulated voltages are ready (bit SVIO) or if VDD_IO has dropped below the brown−out level of 1.3 V (bit SSUM).

In power−down mode the core supply voltages for digital and analog functions are switched off to minimize leakage power. Most register contents are preserved but access to the FIFO is not possible and FIFO contents are lost. SPI access to registers is possible, but at lower speed.

In deep−sleep mode all supply voltages are switched off.

All digital and analog functions are disabled. All register contents are lost. To leave deep−sleep mode the pin SEL has to be pulled low. This will initiate startup and reset of the AX5243. Then the MISO line should be polled, as it will be held low during initialization and will rise to high at the end of the initialization, when the chip becomes ready for operation.

Crystal Oscillator and TCXO Interface

The AX5243 is normally operated with an external TCXO, which is required by most narrow−band regulation with a tolerance of 0.5 ppm to 1.5 ppm depending on the regulation. The on−chip crystal oscillator allows the use of an inexpensive quartz crystal as the RF generation subsystem’s timing reference when possible from a regulatory point of view.

A wide range of crystal frequencies can be handled by the crystal oscillator circuit. As the reference frequency impacts both the spectral performance of the transmitter as well as the current consumption of the receiver, the choice of reference frequency should be made according to the regulatory regime targeted by the application. For guidelines see the separate Application Notes for usage of AX5243 in compliance with various regulatory regimes.

The crystal or TCXO reference frequency should be chosen so that the RF carrier frequency is not an integer multiple of the crystal or TCXO frequency.

The oscillator circuit is enabled by programming the PWRMODE register. At power−up it is enabled.

To adjust the circuit’s characteristics to the quartz crystal being used, without using additional external components, the tuning capacitance of the crystal oscillator can be programmed. The transconductance of the oscillator is automatically regulated, to allow for fastest start−up times together with lowest power operation during steady−state oscillation.

The integrated programmable tuning capacitor bank makes it possible to connect the oscillator directly to pins CLK16N and CLK16P without the need for external

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capacitors. It is programmed using bits XTALCAP[5:0] in register XTALCAP.

To synchronize the receiver frequency to a carrier signal, the oscillator frequency could be tuned using the capacitor bank however, the recommended method to implement frequency synchronization is to make use of the high resolution RF frequency generation sub−system together with the Automatic Frequency Control, both are described further down.

Alternatively a single ended reference (TXCO, CXO) may be used. For detailed TCXO network recommendations depending on TCXO output swing refer to the AX5243 Application Note: Use with a TCXO Reference Clock.

Low Power Oscillator and Wake−on−Radio (WOR) Mode

The AX5243 features an internal lowest power fully integrated oscillator. In default mode the frequency of oscillation is 640 Hz ± 1.5%, in fast mode it is 10.2 kHz

±1.5%. These accuracies are reached after the internal hardware has been used to calibrate the low power oscillator versus the RF reference clock. This procedure can be run in the background during transmit or receive operations.

The low power oscillator makes a WOR mode with a power consumption of 500 nA possible.

If Wake−on−Radio Mode is enabled, the receiver wakes up periodically at a user selectable interval, and checks for a radio signal on the selected channel. If no signal is detected, the receiver shuts down again. If a radio signal is detected, and a valid packet is received, the microcontroller is alerted by asserting an interrupt.

The AX5243 can thus autonomously poll for radio signals, while the micro−controller can stay powered down, and only wakes up once a valid packet is received. This allows for very low average receiver power, at the expense of longer preambles at the transmitter.

GPIO Pin

Pins SYSCLK, IRQ and TCXO_EN can be used as general purpose I/O pins by programming pin configuration registers PINFUNCSYSCLK, PINFUNCIRQ, PINFUNCPWRAMP. Pin input values can be read via register PINSTATE. Pull−ups are disabled if output data is programmed to the GPIO pin.

Figure 5. GPIO Pin

65 kW VDD_IO

VDD_IO

output data

input data

enable weak pull−up

enable output

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SYSCLK Output

The SYSCLK pin outputs either the reference clock signal divided by a programmable power of two or the low power oscillator clock. Division ratios from 1 to 1024 are possible.

For divider ratios > 1 the duty cycle is 50%. Bits SYSCLK[4:0] in the PINFUNCSYSCLK register set the divider ratio. The SYSCLK output can be disabled.

After power−up SYSCLK outputs 1/16 of the crystal oscillator clock, making it possible to use this clock to boot a micro−controller.

Power−on−Reset (POR)

AX5243 has an integrated power−on−reset block. No external POR circuit is required.

After POR the AX5243 can be reset by first setting the SPI SEL pin to high for at least 100 ns, then setting followed by resetting the bit RST in the PWRMODE register.

After POR or reset all registers are set to their default values.

RF Frequency Generation Subsystem

The RF frequency generation subsystem consists of a fully integrated synthesizer, which multiplies the reference frequency from the crystal oscillator to get the desired RF frequency. The advanced architecture of the synthesizer enables frequency resolutions of 1 Hz, as well as fast settling times of 5 – 50 ms depending on the settings (see section AC Characteristics). Fast settling times mean fast start−up and fast RX/TX switching, which enables low−power system design.

For receive operation the RF frequency is fed to the mixer, for transmit operation to the power−amplifier.

The frequency must be programmed to the desired carrier frequency.

The synthesizer loop bandwidth can be programmed, this serves three purposes:

1. Start−up time optimization, start−up is faster for higher synthesizer loop bandwidths

2. TX spectrum optimization, phase−noise at 300 kHz to 1 MHz distance from the carrier improves with lower synthesizer loop bandwidths 3. Adaptation of the bandwidth to the data−rate. For transmission of FSK and MSK it is required that the synthesizer bandwidth must be in the order of the data−rate.

VCO

An on−chip VCO converts the control voltage generated by the charge pump and loop filter into an output frequency.

This frequency is used for transmit as well as for receive operation. The frequency can be programmed in 1 Hz steps in the FREQ registers. For operation in the 433 MHz band, the RFDIV bit in the PLLVCODIV register must be programmed.

The fully integrated VCO allows to operate the device in the frequency ranges 800 – 1050 MHz and 400 – 525 MHz.

The carrier frequency range can be extended to 54 – 525 MHz and 27 – 262 MHz by using an appropriate external inductor between device pins L1 and L2. The bit VCO2INT in the PLLVCODIV register must be set high to enter this mode.

It is also possible to use a fully external VCO by setting bits VCO2INT = 0 and VCOSEL = 1 in the PLLVCODIV register. A differential input at a frequency of double the desired RF frequency must be input at device pins L1 and L2. The control voltage for the VCO can be output at device pin FILT when using external filter mode. The voltage range of this output pin is 0 – 1.8 V.

This mode of operation is recommended for special applications where the phase noise requirements are not met when using the fully internal VCO or the internal VCO with external inductor.

VCO Auto−Ranging

The AX5243 has an integrated auto−ranging function, which allows to set the correct VCO range for specific frequency generation subsystem settings automatically.

Typically it has to be executed after power−up. The function is initiated by setting the RNG_START bit in the PLLRANGINGA or PLLRANGINGB register. The bit is readable and a 0 indicates the end of the ranging process.

Setting RNG_START in the PLLRANGINGA register ranges the frequency in FREQA, while setting RNG_START in the PLLRANGINGB register ranges the frequency in FREQB. The RNGERR bit indicates the correct execution of the auto−ranging.

VCO auto−ranging works with the fully integrated VCO and with the internal VCO with external inductor.

Loop Filter and Charge Pump

The AX5243 internal loop filter configuration together with the charge pump current sets the synthesizer loop band width. The internal loop−filter has three configurations that can be programmed via the register bits FLT[1:0] in registers PLLLOOP or PLLLOOPBOOST the charge pump current can be programmed using register bits PLLCPI[7:0] in registers PLLCPI or PLLCPIBOOST. Synthesizer bandwidths are typically 50 – 500 kHz depending on the PLLLOOP or PLLLOOPBOOST settings, for details see the section: AC Characteristics.

The AX5243 can be setup in such a way that when the synthesizer is started, the settings in the registers PLLLOOPBOOST and PLLCPIBOOST are applied first for a programmable duration before reverting to the settings in PLLLOOP and PLLCPI. This feature enables automated fastest start−up.

Setting bits FLT[1:0] = 00 bypasses the internal loop filter and the VCO control voltage is output to an external loop filter at pin FILT. This mode of operation is recommended for achieving lower bandwidths than with the internal loop filter and for usage with a fully external VCO.

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Table 17. REGISTERS

Register Bits Purpose

PLLLOOP PLLLOOPBOOST

FLT[1:0] Synthesizer loop filter bandwidth and selection of external loop filter, recommended usage is to increase the bandwidth for faster settling time, bandwidth increases of factor 2 and 5 are possible.

PLLCPI PLLCPIBOOST

Synthesizer charge pump current, recommended usage is to decrease the bandwidth (and improve the phase−noise) for low data−rate transmissions.

PLLVCODIV REFDIV Sets the synthesizer reference divider ratio RFDIV Sets the synthesizer output divider ratio VCOSEL Selects either the internal or the external VCO

VCO2INT Selects either the internal VCO inductor or an external inductor between pins L1 and L2 FREQA, FREQB Programming of the carrier frequency

PLLRANGINGA, PLLRANGINGB Initiate VCO auto−ranging and check results

RF Input and Output Stage (ANTP/ANTN)

The AX5243 antenna interface uses differential pins ANTP and ANTN for both RX and TX. RX/TX switching is handled internally.

LNA

The LNA amplifies the differential RF signal from the antenna and buffers it to drive the I/Q mixer. An external matching network is used to adapt the antenna impedance to the IC impedance. A DC feed to GND must be provided at the antenna pins. For recommendations see section:

Application Information.

PA

In TX mode the PA drives the signal generated by the frequency generation subsystem out to either the differential antenna terminals or to the single ended antenna pin. The antenna terminals are chosen via the bits TXDIFF and TXSE in register MODECFGA.

The output power of the PA is programmed via the register TXPWRCOEFFB.

The PA can be digitally pre−distorted for high linearity.

The output amplitude can be shaped (raised cosine), this mode is selected with bit AMPLSHAPE in register

MODECFGA. PA ramping is programmable in increments of the bit time and can be set to 1 – 8 bit times via bits SLOWRAMP in register MODECFGA.

Output power as well as harmonic content will depend on the external impedance seen by the PA, recommendations are given in the section: Application Information.

Digital IF Channel Filter and Demodulator

The digital IF channel filter and the demodulator extract the data bit−stream from the incoming IF signal. They must be programmed to match the modulation scheme as well as the data−rate. Inaccurate programming will lead to loss of sensitivity.

The channel filter offers bandwidths of 995 Hz up to 221 kHz.

The AX−RadioLab Software calculates the necessary register settings for optimal performance and details can be found in the AX5243 Programming Manual. An overview of the registers involved is given in the following Table 18 as reference. The register setups typically must be done once at power−up of the device.

Table 18. REGISTERS

Register Remarks

DECIMATION This register programs the bandwidth of the digital channel filter.

RXDATARATE2… RXDATARATE0 These registers specify the receiver bit rate, relative to the channel filter bandwidth.

MAXDROFFSET2… MAXDROFFSET0 These registers specify the maximum possible data rate offset.

MAXRFOFFSET2… MAXRFOFFSET0 These registers specify the maximum possible RF frequency offset.

TIMEGAIN, DRGAIN These registers specify the aggressiveness of the receiver bit timing recovery. More